The present disclosure relates to implantable neurostimulator devices and systems, for example, cochlear stimulation systems, and to strategies for storing parameters employed in conjunction with such systems.
Prior to the past several decades, restoring hearing to the deaf was generally believed to be impossible. More recently, however, scientists have had increasing success in restoring normal hearing in subjects affected by substantial hearing loss. In some cases, hearing loss can be overcome through electrical stimulation. For example, electrical signals can be applied to the auditory nerve, bypassing damaged cochlear hair cells that may be disrupting hearing. Initial attempts to restore hearing using this type of technique were not very successful, because some patients were still unable to understand speech. Over time, however, the auditory sensations elicited by electrical stimulation gradually came closer to approximating normal speech. Electrical stimulation of the auditory nerve can be implemented through a prosthetic device, commonly referred to as a cochlear implant, which is surgically implanted into a subject affected by hearing loss.
Cochlear stimulation systems, such as the systems described in U.S. Pat. Nos. 5,938,691 and 6,219,580, each of which is incorporated herein by reference, produce sensations of sound in patients affected by hearing loss through direct stimulation of the ganglia of the auditory nerve cells. Cochlear stimulation systems are generally comprised of several components, including an electrode array that incorporates one or more electrode pairs, an implantable cochlear stimulator, an externally wearable speech processor (or signal processor) with one or more microphones, and a communication path that couples the external speech processor and the implantable cochlear stimulator through the skin, such as a radio frequency link. The external portion of the communication pathway can be incorporated into a headpiece that can be affixed and aligned with the implantable cochlear stimulator, such as through the use of one or more magnets. Alternatively, the external portion of the communication pathway can be integrated into the speech processor, which can be affixed adjacent to the pinna in proximity to the implantable cochlear stimulator.
The acoustic signals received by the one or more microphones included in the cochlear stimulation system are transformed into sound data by the speech processor. The sound data can then be transferred to the implantable cochlear stimulator, such as by transmission over the communication pathway. Once received in the implantable cochlear stimulator, the sound data can be used to selectively generate the electrical stimuli that are directed to one or more cochlea stimulating channels, each of which is associated with one or more electrodes or electrode pairs included within the electrode array.
Within the cochlea, there are two main cues that convey “pitch” (frequency) information to the listener. They are (1) the place or location of stimulation along the length of the cochlear duct and (2) the temporal structure of the stimulating waveform. Specific frequencies of sound are detected by specific portions of the cochlea, such that each frequency is mapped to a particular location along the cochlea. Generally, from low to high, sound frequencies are mapped from the apical to the basilar direction. Accordingly, the electrode array can be fitted to a patient to arrive at a mapping scheme such that electrodes near the base of the cochlea are stimulated with high frequency signals, while electrodes near the apex are stimulated with low frequency signals. Thus, the stimulation signals provided to the electrodes model the received acoustic signal associated with a particular frequency band.
Several different strategies have been developed for processing detected acoustic signals and transforming them into electrical stimuli that can be applied to the cochlea. These strategies, often referred to as speech processing strategies, define a pattern of electrical waveforms that can be applied as controlled electrical currents to the one or more cochlea stimulating channels associated with the electrode array. Speech processing strategies can be broadly classified as: (1) sequential or non-sequential pulsitile stimulation, in which only one electrode receives an electrical pulse at a time; (2) simultaneous pulsitile stimulation, in which substantially all of the electrodes receive electrical pulses at the same time, approximating an analog signal; or (3) partially simultaneous pulsitile stimulation, in which only a select grouping of electrodes receive electrical pulses at the same time and the electrical pulses are received in accordance with a predefined pattern.
It also is possible to further divided these strategies based on the waveform of the electrical stimuli, i.e., whether the electrical stimuli is an analog waveform or a biphasic (or multiphasic) waveform. Generally, analog waveforms represent filtered versions of a continuous acoustic signal, such as the signal received by a microphone. Analog waveforms are typically reconstructed by the generation of continuous, short, monophasic pulses or samples. The rate at which the samples are taken from a continuous acoustic signal must be high enough to permit the accurate reconstruction of the temporal details of the continuous acoustic signal. If an analog signal is not sampled at a sufficiently high rate, artifacts may result. Biphasic (or multiphasic) pulses, commonly referred to as pulsitile waveforms, typically include a single cycle of a square wave in which current flows in one direction at a particular magnitude and for a particular time, followed by a current flow in the opposite direction at a similar magnitude and for a similar period of time.
There are numerous other stimulation patterns known in the art that may be formulated. One simulation pattern may prove more effective for a particular patient than any other stimulation pattern, since each patient may respond differently to a particular speech processing strategy. The complex biophysical phenomenon associated with the electrical stimulation of neurons and psychophysical phenomena regarding the interpretation of neural activity by the auditory nervous system suggest that the quality and intelligibility of speech precepts evoked by a cochlear stimulation system may be improved in a given patient by more specific manipulations of the electrical stimuli tailored to that patient. Stimulation strategies are described in further detail in U.S. patent application Ser. No. 11/226,777, which is incorporated herein by reference. Identifying which of the available speech processing and stimulation strategies is most beneficial for a given patient is commonly performed at the fitting stage.
A specialist, such as an audiologist, generally customizes or “fits” a newly provided cochlear stimulation system to a patient. In fitting the cochlear stimulation system, the specialist selects the modes and methods of operation that will be used by the system to help the patient perceive sound. The modes and methods include information defining the general processing characteristics, such as parameters utilized by the speech processor. Additionally, the modes and methods include patient-specific information, such as stimulation parameters and settings. Although the specialist can exercise a substantial amount of control and discretion in selecting the modes and methods of operation, the specialist typically employs a fitting system to properly customize the cochlear stimulation system to meet the individual needs of a patient. Fitting systems are described in further detail in U.S. Pat. Nos. 5,626,629 and 6,289,247, both of which are incorporated herein by reference.
Once they have been determined, the modes and methods of operation can be stored in the cochlear stimulation system for use in configuring the device each time it is initialized, which generally occurs whenever the external portion of the unit is powered off or disconnected from the patient. During initialization, one or more items of information can be transmitted between the speech processor portion and the implantable cochlear stimulator. In the implantable cochlear stimulator, information can be stored in a random access memory for use during operation. For example, a speech processor can be configured to detect the presence of an implantable cochlear stimulator and, upon such detection, communicate with the implantable cochlear stimulator to configure the cochlear stimulation system for operation. Further, the speech processor can include one or more user controls, which can be used to configure the implantable cochlear stimulator. Once configured, the implantable cochlear stimulator can use the patient specific parameters to generate the electrical stimuli that are applied to one or more cochlea stimulating channels. When configured to use one or more parameters stored in a volatile memory, an implantable cochlear stimulator can be periodically monitored during operation. Alternatively, the implantable cochlear stimulator can be configured to notify the speech processor of any change in configuration.